Development,settling behaviour,metamorphosis and pentacrinoid feeding and growth of the feather star Florometra serratissima

Embryonic development of the northeastern Pacific feather star Florometra serratissima takes place within a ridged fertilization membrane. Cleavage is radial, resulting in a coeloblastula, and gastrulations is by invagination. Cilia are swollen terminally during ciliogenesis whereas fully grown cilia possess several swellings along the length of their shafts. Young doliolaria larvae begin to hatch from the fertilization membranes 35 h after fertilization (9.5° to 11.5°C); by 4 d the doliolaria has acquired ciliated bands, a vestibular invagination and an antero-ventral adhesive pit. The surface of the larva is covered with a delicate glycocalyx supported by microvilli. Larvae swim along a vertical sinusoidal path just below the water surface; they begin to explore the substratum at 4.5 d and settlement begins as early as 4.6 d, but can be delayed for up to 9 more days. Larvae settle gregariously in culture and it is suggested that gregarious settlement plays a role in the formation and maintenance of adult aggregations of F. serratissima. Metamorphosis into a stalked cystidean following settlement is rapid. Major changes at this period include: loss of cilia; withdrawal of ectoderm from the glycocalyx; covering over of the vestibular invagination; and a 90 degree rotation of the vestibule to the former posterior end of the doliolaria. Transformation from cystidean to pentacrinoid includes the opening of the 5 oral plates, the extension of the 15 papillate tube feet and further elongation of the stalk. The pentacrinoid is able to feed on small food particles. Rudiments of all 10 adult arms are present by 4 months; at 6 months the pentacrinoid has an arm span of 6.5 mm but cirri and pinnules are not yet present.